docs: def get_summary_data(self, group_name):
          """ Get the summary data for an analysis group.
          
          :param group_name: The name of the analysis group to pull summary
              data for.
          :returns: A dictionary whose keys are analysis steps, and whose
              values are dictionaries of key/value pairs for the results of
              that step.
          """
          self.assert_open()
          group = 'Analyses/{}/Summary'.format(group_name)
          summary = None
          if group in self.handle:
              summary = self._parse_attribute_tree(group)
          return summary